1. Field of the Invention
The present invention relates to the assembly in a single electronic device of a plurality of circuit components, and more particularly to the compact assembly of such circuit components in close proximity one with another in a three-dimensional spatial relationship.
2. Background Art
Complex electronic devices usually unvolve a plurality of distinct circuit components which must be electrically interconnected in order to achieve the objectives of the device. Increasingly, such circuit components are themselves complex electrical subsystems, taking the form of integrated circuit semiconductor chips. Whether interconnecting semiconductor chips or discrete circuit components of the traditional type, every effort is made to place such circuit constituents in close proximity one to another. This is undertaken in order to reduce the overall size of the electronic device which the circuit constituents comprise, to reduce the quantity of electrically conductive material required to effect interconnection of the circuit constituents, and preferably to group together in a standard, electrically interconnected arrangement circuit constituents that together perform an identifiable electrical function. In high speed electronic devices the separation between circuit components is minimized in order to reduce the time required for signals to be communicated between those devices.
Typically, plural circuit components are electrically interconnected by their attachment to conductive pads or contact apertures on a rigid planar printed circuit board. Where the circuit components are of the traditional discrete variety, soldering, fusion, or the application of conductive paste, epoxy, elastomer, or cement to conductive surfaces on an individual basis is required in order to effect this attachment. Because of the small size and large number of leads, wires, or connection points involved in the typical integrated circuit semiconductor chip, however, such devices are not always attached to printed circuit boards directly.
Integrated circuit semiconductor chips are traditionally mounted on, embedded in, or attached to a semiconductor chip carrier package having electrical insulating capability. Electrically conductive pathways comprising variously pins, wires, or printed conductive routing traces are electrically connected to contact points on the integrated circuit semiconductor chip and extend therefrom to the exterior of the carrier package. The pins, wires, traces, or other electrical contact points on the exterior of the package or carrier may then be inserted into sockets in receptacle housings, or chips, which have already been secured to the circuit board and electrically interconnected to the conductive routing traces thereon. Such integrated circuit semiconductor chip carrier packages may also be attached or electrically interconnected directly to conductive pads and apertures on the printed circuit board by the methods mentioned above in relation to the attachment of traditional discrete circuit components to circuit boards.
While the process of inserting a semiconductor chip carrier package into a receptacle housing is not particularly arduous, the securing of such receptacle housings or the semiconductor chip carrier packages directly to a circuit board can be quite tedious and time consuming. In many instances advanced robotics or other automated methods of drilling and attachment must be employed.
As the number of circuit components in an electronic device increases, the size and complexity of the printed circuit board to which the circuit components are attached is similarly affected. This results in the need for multiple layers of conductive traces in the circuit board employed. The physical separation between circuit components also increases, particularly between those components at the opposite ends of the same sides of the circuit board, lengthening the conductive routing traces electrically connecting the circuit components. Signal delay, heat dissipation, and fabrication complexity thereby become potential problems.
If the expanse of the circuit board required exceeds the area allocated for it in the housing of the overall device, then a complementing assembly strategy is employed. This involves the design and fabrication of a plurality of distinct circuit boards mounted over or next to one another on posts, or inserted by the edges thereof into some other form of upstanding support bus or channel. Electrical interconnection between such circuit boards is generally achieved through the support structure therebetween.
Nevertheless, in such arrangements each circuit board with its own plurality of attached circuit components projecting from the surface thereof is a delicate article to handle, assemble, or service. Space must be maintained between each of the circuit boards to accommodate for the circuit components attached thereupon. Such a method of circuit component assembly is disclosed in U.S. Pat. No. 2,907,926.
While the electrical interconnection of circuit components on a single circuit board is substantially two-dimensional in nature, the stacking of circuit boards in the manner described introduces among the circuit components involved a third dimension in which that interconnection can occur, one normal to the planes of the circuit boards. In this third dimension electrical interconnections can be effected, potentially rendering the conductive trace patterns on the circuit boards themselves less complex and advantageously reducing the average electrical distance among circuit components by shortening the length of some interconnecting traces. Signal transfer times between some circuit components can possibly be kept within smaller limits than with other methods of circuit component assembly. This is particularly advantageous in complex electronic devices.
Nevertheless, while the circuit component assembly technique illustrated in U.S. Pat. No. 2,907,926 does enable a circuit designer to place a large number of circuit components in close spatial relation one to another, that technique remains limited by the disadvantages inherent in its traditional use of printed circuit boards. As mentioned earlier, these include the difficulty of attaching components to circuit boards and the fragility of the resulting structure with those components projecting from the surface thereof. The complexity of fabrication and assembly associated with this method is also greatly increased.
This latter aspect of circuit board utilization requires the maintenance between each circuit board of a substantial volume of unused space so that circuit components attached to one circuit board will not encounter those on an adjacent board. Additionally, auxiliary support structures must be interposed between circuit levels to hold the circuit board layers apart from one another. As a result, space in electronic devices is not maximally utilized. These considerations limit the capacity of stacked circuit board arrangements to densify the circuit components involved.
Alternatively U.S. Pat. No. 4,510,551 discloses the use of a flexible printed circuit board to which circuit components are mounted in columns on conductive pads arrayed in parallel lines in the traditional manner. The circuit board is then rolled upon itself with an insulation layer interposed therebetween about an axis parallel to the lines of those conductive pads, producing a spatially compact cylindrical arrangement of electrical circuit components. A rigid cylindrical housing encloses the rolled circuit board to maintain its physical integrity.
Despite the close spatial relationship that results among circuit components in this circuit component assembly, the interconnection between circuit components is limited to the use of conductive routing traces in the two-dimensional plane of the unrolled circuit board. Accordingly, while some spatial densification of the circuit components mounted on the circuit board can be effected in this manner, those components remain in an electrical sense as remote from one another as if mounted on a rigid planar circuit board. Components at remote ends of the board, while possibly close together in a spatial sense once the board is rolled up, are still separated electrically by conductive traces that must traverse the full length of the circuit board. The method disclosed is also still affected by the disadvantages of the traditional way in which circuit components are attached to circuit boards, and the fragility of the circuit board with the attachments thereto continues to inhibit easy assembly and maintenance.